260 with 140 bergers

I loaded up some loads for testing this past weekend and am kinda baffled. Starting charge was 41grains H4350 and went up to 43grains in half grain increments.Ten rounds for each charge.Shot 5 shot groups of each charge at 300 meters.Smallest groups was 3".That was with 42grains.The rest were worse.Was very disapointed. Our range goes to 600 yards and has a gong.So i decided just for the heck of it to test the last rounds of 5 each of each charge out at 600 on the gong.This is where i am baffled.The charge with 42 grains grouped into 1 1/4".This is from outside of crater to outside of crater.42.5 grains was a little bigger than 42 grains.I know the term bullet going to sleep but does it take that long?
I didn't chronograph any of these loads.
conditions weren't the greatest.There was a stiff wind from 4:00 at about 15-20mph.I am very happy with the results just looking for possible reasons of this.
The gun is a faactory Rem 700 24"stainless steel sporter weight.Not bedded with a jewell trigger.Shot off bags on the bench.Each shot was shot the same ie,pressure,hold and so on.
Any clues?
Thanks
Matt

Sorry i put this in the wrong place.I meant to put it in the ballistics one.